The present invention relates to a current-limiting contact arrangement including a stationary contact, a contact arm having a movable contact which can be brought into and out of contact with the stationary contact, and an arc control device having arc splitters. Contact arrangements of this kind are used, for example, in low-voltage switchgear such as circuit-breakers, miniature circuit-breakers, or motor protection switches.
European Patent Document No. EP-B-0419324 describes a current-limiting contact arrangement composed of two stationary conductor rails which each have one stationary contact and of a contact bridge having two movable contacts which are to be brought into and out of contact with the stationary contacts for closing and opening an electric circuit. The conductor rails each have two current loops extending on both sides along the opening travel of the movable contacts and in planes running parallel to the longitudinally running center plane of the contact arrangement. When the contacts are electrodynamically opened in response to a high short-circuit current, the inductive effect of the short-circuit current flowing through the current loops causes the arcs forming between the opening contacts to be deflected in such a way that they are diverted in an accelerated manner along arc diverters which are connected to the conductor rails and a shared arc diverter which is situated at a distance therefrom, resulting in the extinction of the arcs. The conductor rails, the arc diverters, the guide for the contact bridge as well as a contact pressure spring are supported in the preassembled condition in a centrically arranged insulating base and in insulating shells which are arranged on both sides thereof and parallel to the mentioned center plane, the current loops being received by the outer walls of the insulating shells. This contact arrangement which, on each side, is provided with one arc quenching gap opening toward the outside is received by suitably designed inner surfaces of a switching device enclosure in a positive locking manner. The preassembly of the contact arrangement which requires considerable outlay constitutes a disadvantage. Also described is a contact arrangement composed of a conductor rail featuring a current loop and an arc diverter and of a swivelling contact arm having an arc-diverting horn; however, no details are given on the assembly of this contact arrangement.
European Patent Document No. EP-A-0231600 describes a current-limiting contact arrangement of the species which is composed of a fixed conductor rail featuring a stationary contact and having an arc diverter, of a contact arm having a movable contact, and of an arc control device in the form of an arc splitter pack. The conductor rail features two current loops extending on both sides along the only initial opening travel of the movable contacts and in a curved plane running perpendicularly to the center plane of the contact arrangement. An insulating part is to be slid over the current loops to prevent an arc forming between the opening contacts in the event of a short-circuit current from arcing over to the current loops and which holds an insulated magnet yoke which is to be arranged above current loops and whose magnetic field drives the arc into the quenching device in an accelerated manner over the remaining opening travel of the movable contact. The conductor rail featuring the insulating part, the magnet yoke, and the arc splitter pack are to be mounted individually in a switching device enclosure; no provision is made for a preassembly. A further disadvantage consists in the need for the magnet yoke and in the relatively large width of the contact arrangement necessitated by the shape of the current loops.
Therefore, an object of the present invention is to provide a contact arrangement which saves space and is favorable from a standpoint of production engineering.
The present invention provides a current-limiting contact arrangement including a conductor rail featuring a stationary contact and having two current loops extending at both sides along the center plane of the contact arrangement, a contact arm having a movable contact which can be brought into and out of contact with the stationary contact, as well as an arc control device having arc splitters. The current loops extend in planes parallel to the center plane and along the entire opening travel of the movable contact. Provision is made for a two-part cassette made of insulating material, the arc splitters being retained in a positive-locking manner in the interior thereof, and the part of conductor rail linked with the stationary contact and the contact arm reaching into the interior thereof, and the current loops being retained in a positive-locking manner at the outer walls thereof. The combination of the cassette provided with the arc splitters and of the conductor rail is received in a positive-locking manner by suitably designed inner surfaces of a switching device enclosure.
Through the accommodation and the positive-locking affixation of the immovable contact elements and of the arc splitters by the two-part cassette, a preassembled subassembly is provided which can be easily inserted into the switching device enclosure. The alignment of the current loops parallel to the center plane and their fixing and insulation against the remaining contact parts by the cassette gives rise to a compact contact arrangement of a small width which, by being relatively enclosed, provides for a favorable flow behavior of the arcing gasses inside, the developing pressure being intercepted in such a manner that material stressing is avoided because of the positive-locking accommodation of the cassette in the switching device enclosure. Due to the substantially enclosed cassette design, moreover, the insulation resistance between non-connected live parts is considerable.
By supporting the cassette all-round, it becomes considerably easier to intercept the internal pressure arising during the occurrence of arcs. The switching device enclosure is preferably composed of a lower-quality insulating material since a noticeable part of the mechanical stress and the greatest part of the thermal stress is taken up by the cassette. The ease of assembly of the cassette subassembly is further improved by the capability of both cassette parts of being snap-connected.
The cassette may be composed of a chamber part which is provided with an exhaust port and used for receiving the arc splitters as well as of cover part which is provided with a passage aperture and used for fixing the arc splitters and for the contact arm, very large clearances and leakage distances between non-connected live parts being formed by the partially nested cassette parts and by the narrow design of the passage aperture.
The arc splitters are preferably retained between strip-like formations of the joined cassette parts. The alignment of these formations and possibly of additional formations or recesses for fixing additional parts in the direction of the molds to be removed leads to a considerable simplification of the molding process.
It is sufficient and favorable for reasons of insulation resistance if the conductor rail reaches into the interior of the cassette through one of the cassette parts only with the stationary contact member. Outer guiding strips ensure a reliable and definite support of the current loops. In terms of manufacture, it is particularly favorable for the current loops to be slid onto the cassette in a straight line.
In the cassette, a stop for intercepting the kinetic energy of the contact arm which is electrodynamically thrown open in the event of a short circuit can easily be affixed inside the cassette. In addition to the arc splitters or in lieu of the arc splitters, insulating parts can be retained in the cassette by suitable formations, the insulating parts releasing quenching gasses during the occurrence of arcs.